1. Field of the Invention
This invention relates to a magnetic recording medium having a ferromagnetic metal layer as a magnetic recording layer and more particularly, it is concerned with a magnetic recording medium having a good surface smoothness, high output and low noise.
2. Description of the Prior Art
Up to the present time, magnetic recording media of binder type have widely been used in which a powdered magnetic material such as .gamma.-Fe.sub.2 O.sub.3, Co-doped Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, Co-doped Fe.sub.3 O.sub.4, Berthollide compounds of .gamma.-Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4, CrO.sub.2 and ferromagnetic alloy powders is dispersed in an organic binder such as vinyl chloride-vinyl acetate copolymers, styrene-butadiene copolymers, epoxy resins and polyurethane resins, coated onto a non-magnetic support and dried. Of late, on the other hand, magnetic recording media of the so-called non-binder type have become worthy of notice, in which no binder is used and a magnetic recording layer consisting of a ferromagnetic metal thin film is formed by the vapor deposition method such as vacuum evaporation, sputtering or ionic-plating, or by the plating method such as electroplating or electroless plating, as requirements for high density recording have rised, and various efforts have been made for the purpose of realizing the recording media of this type.
In the case of using these magnetic recording media as a magnetic tape, the relative speed of the tape and a reproducing head is usually 38 cm/sec for video signal recording (video tape recorder (VTR) for broadcasting), 11.1 m/sec for EIJA (Electronic Industries Association of Japan) Type I VTR, 10.4 m/sec, 7.8 m/sec and 6.9 m/sec for Small type VTR and, for audio signal recording, it is usually 38 cm/sec, 19 cm/sec and 9.5 cm/sec in open reel tapes and 9.8 cm/sec, 4.76 cm/sec and 2.38 cm/sec in cassette tapes.
Since in the prior art magnetic recording media of binder type, metal oxides having a smaller saturation magnetization than ferromagnetic metals are mainly used as a magnetic material, the thickness reduction required for high density has reached a limit because of resulting in lowering of the signal output and complicated processings and large special installations to recover the solvent and to prevent the public hazards are required for the production of such magnetic recording media. On the contrary, the magnetic recording media of non-binder type have advantages that the process for the production thereof is simple and an extreme thickness reduction is possible because a ferromagnetic metal having a larger saturation magnetization than metal oxides is formed as a thin film under such a state as being free from non-magnetic materials such as binders.
Magnetic recording media having a ferromagnetic metal layer as a magnetic recording layer have hitherto been considered to be suitable for high density recording, in particular, recording of short wavelengths of about 1 .mu.m such as video signals, but, in the prior art magnetic recording media having a ferromagnetic metal layer, the output of video signals within a range of short recording wavelengths is not always so high as expected and noise level is considerably high. Therefore, these magnetic recording media are inferior to the prior art magnetic recording media of binder type in S/N ratio in some cases.